Non-contact viscous material dispensers are often used to apply minute amounts of viscous materials, i.e. those with a viscosity exceeding fifty centipoise, onto substrates. As used herein, “non-contact” means where the jetting dispenser does not contact the substrate during the dispensing process. For example, non-contact jetting dispensers are used to apply various viscous materials onto electronic substrates like printed circuit boards. Viscous materials applied to electronic substrates include, by way of example and not by limitation, general purpose adhesives, solder paste, solder flux, solder mask, thermal grease, lid sealant, oil, encapsulants, potting compounds, epoxies, die attach fluids, silicones, RTV, and cyanoacrylates.
Specific applications abound for dispensing viscous materials from a non-contact dispenser onto a substrate. In semiconductor package assembly, applications exist for underfilling, solder ball reinforcement in ball grid arrays, dam and fill operations, chip encapsulation, underfilling chip scale packages, cavity fill dispensing, die attach dispensing, lid seal dispensing, no flow underfilling, flux jetting, and dispensing thermal compounds, among other uses. For surface-mount technology (SMT) printed circuit board (PCB) production, surface mount adhesives, solder paste, conductive adhesives, and solder mask materials may be dispensed from non-contact dispensers, as well as selective flux jetting.
Jetting dispensers generally contain either pneumatic or electric actuators for moving a shaft or tappet repeatedly toward a seat while jetting a droplet of viscous material from an outlet orifice of the dispenser. The electrically actuated jetting dispensers can, more specifically, use a piezoelectric actuator. Precisely jetting fluids using a valve closure structure contacting a valve seat requires that the shaft be brought into contact with the valve seat using a prescribed stroke (displacement) and velocity to effectively eject a dot of fluid material from the outlet of the nozzle. The displacement and velocity curve collectively form the motion profile. The stroke, velocity, and sealing force are best controlled when the point of impact between the valve closure structure and the valve seat is precisely known and measured. There must be sufficient force after the impact of the shaft with the valve seat to create a seal to prevent leakage of the fluid material. However, too much force will result in excess wear, or even damage, to the components.
Changes of only a few micrometers affect the performance of the fluid dispenser. Typically, these adjustments are performed manually by a user through mechanical means, such as adjusting a screw. This manual process takes multiple iterations yet still fails to precisely adjust the motion profile for the desired performance. Therefore, there exists a continuing need to determine the position of the valve closure structure relative to the valve seat to optimize performance and settings of the fluid dispenser, and adjust the motion profile of the fluid dispenser accordingly.
For at least these reasons, it would be desirable to provide a jetting system and method that addresses these and other issues.